Temperatures once again reached 90 degrees across most of southern Michigan this afternoon with several hitting 91 thus far. Today will end the record heat wave as a cold front will sweep through Wednesday morning finally pushing the dominate ridge south and east out of the area. The front will bring a very small chance of rain late tonight into Wednesday morning. It will also drop high temperatures by about 20 degrees with temps likely failing to hit 70 Thursday through Sunday.

The developing low over western Upper Michigan will continue to deepen slightly while lifting NE on the nose of the strengthening 850mb low level jet. The front becomes more progressive toward Wednesday morning as a strong upper level jetlet ejects out of the base of the trough through the plains and into the region and the next lobe of vorticity rotates around the upper low over central Canada. While the wind shift sweep through around 09-12z Wednesday, the surface front will lag a few hours behind, with the actual cold advection holding off further yet toward til after 18z.

Rain chances tonight as still looking bleak as commented on by previous forecasters, but still exists tonight. There will be a few hour window mainly between 09-14z where the passing prefrontal band could ignite a few showers. As mentioned, the low and related forcing will be lifting NE low level jet should stay north and west of the local area. Fropa at the diurnal minimum will not help its cause with cape only forecast to be a couple hundred j/kg Max. Narrow corridor of Theta E ahead of the front. All in all expect a few showers, or a scattered line, moving through northern Michigan possibly extending south to fnt. Chance or slight chance pops will cover The Thumb north of about I-69.

The frontal timing and late push with colder air will allow the Detroit area to reach near 80 degrees Wednesday before temps start to fall. Conversely, with the early frontal timing to the NE, expect locations north of ptk to stay in the 70s. 850mb temps will fall from the current 17-18c today, down into the low single digits by Thursday. Broad troughing aloft along with surface high pressure sliding in keeping cool northerly flow, will keep high temperatures likely in the 60s for all locations Thursday.

A potent upper level wave will drop through the region on Friday bringing a chance for showers throughout the day along with a reinforcing shot of cool air as 850 mb temperatures will remain from 3 to 5 c through much of the weekend. While surface high pressure and ridging building into the region on Saturday will bring mostly sunny skies, the aforementioned cooler air mass will limit highs to the lower to mid 60s on Saturday. With high pressure centered over the region on Saturday night, outlying areas will have the potential to see low temperatures dropping into the upper 30s.

As the ridge axis and surface high pressure moves eastward Sunday into Monday, increasing southwesterly flow will advect warmer air into the region as highs reach the mid to upper 60s on Sunday and low to mid 70s on Monday. Another wave will bring the potential for showers late Monday into Tuesday before stronger ridging looks to build into the region keeping above normal temperatures in place into next week.

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Marine...

Pattern change will occur over the central Great Lakes during the next 24 hours as a cold front pushes through the region. Scattered shower and thunderstorms will be possible over the Northern Lake Huron basin later tonight, but chances will lower appreciably in closer proximity to southeastern Michigan. Strengthening gradient winds are expected to push across the far Northern Lake Huron basin, where west to northwest winds of 30 knots are likely. Cold advection and unstable conditions will allow significant wave heights to increase greater than 5 ft for much of the nearshore waters of Lake Huron. Small craft advisories have been issued Wednesday for outer Saginaw Bay and nearshore waters of Lake Huron from Port Austin southward to Port Huron. High pressure will settle over the region Thursday followed quickly by another low pressure system and cold front due Friday. This system will bring a reinforcement of colder air and unstable marine conditions Friday and Friday night before rapid improvement occurs with high pressure during the weekend.

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Previous discussion... issued at 202 PM EDT Tue Sep 26 2017

Aviation...

Upper level ridging will hold for another 12 to 18 hours across southeastern Michigan before a cold front finally pushes across the area. Until then, looking at persistence of VFR conditions with weak southwesterly winds. The wind shift is expected to push across the area in the 09-12z timeframe with the cold front itself likely lagged. The advent of cold advection may lead to a period of MVFR and potential IFR with a high likelihood for dry conditions along the front.

For dtw... VFR through much of tonight with light wind. There uncertainty regarding overall likelihood for MVFR and IFR Post wind shift or cold front at 11z. Feeling is still higher confidence for MVFR by the late morning.

//Dtw threshold probabilities...

* moderate for ceiling 5000 ft or less but not until late Wednesday morning.